Cyperus esculentus control with glyphosate : time of application and addition of ammonium sulfate PublicDeposited

Descriptions

Cyperus esculentus L. var. esculentus is a serious weed
problem in northwest Spain. Long-term control from glyphosate and
other herbicides has been inconsistent. Field, greenhouse, and
laboratory studies were conducted on factors influencing the
activity of glyphosate on C. esculentus.
In field studies, glyphosate controlled foliage growth at most
growth stages. Number and weight of new tubers were reduced by
glyphosate treatment. Reinfestation the following year was reduced
most by treatments made when new tubers were beginning to form,
thus creating a strong "sink," toward which sugars and glyphosate
translocated. Later applications, when tubers were mostly mature,
were less effective.
A method was developed that involved marking and comparing
growth of new and old leaves in order to measure short-term effects
from glyphosate. This method was non-destructive, easier, and gave
more consistent results than measuring fresh weights.
Several studies on the effect of adding ammonium sulfate to glyphosate solutions have been reported previously. Results have
been varied. In my studies, the addition of ammonium sulfate to
glyphosate solution sometimes caused a greater reduction in leaf
growth on ashort-term basis. This was especially true when leaves
were washed 3 h following treatment or when glyphosate was mixed
with simazine or calcium chloride. The ammonium sulfate overcame a
slight antagonistic effect from the calcium chloride.
The effect of ammonium sulfate on glyphosate translocation was
studied by treating the distal 10 cm of two leaves and removing
the treated portions 1day later. Growth of the remaining leaves
was measured. The addition of ammonium sulfate reduced the effect
of glyphosate on untreated leaves, indicating that the ammonium
sulfate had inhibited glyphosate translocation. Studies with "C-glyphosate
indicated that ammonium sulfate increased the rate of
glyphosate absorption, but did not affect total absorption. Glyphosate translocation from treated portions of the plant was not
significantly affected. These results tend to support the concept
of adding ammonium sulfate to aglyphosate solution when treating
annual weeds, especially when using hard water, but there appears
to be no advantage from adding ammonium sulfate when treating C.
esculentus.